Abstract:

Provided is an injection nozzle and a molding apparatus which ensure
injection pressure by suppressing resin leakage even when a resin
material having a low viscosity is used. In injection molding, it is
especially important that the injection nozzle and a fixed die are
excellently kept in contact with each other and that the resin is not
leaked. Resin leakage from between the injection nozzle and the fixed die
lowers molding pressure, increases molding shrinkage of the resin, and
directly affects the qualities of a molded product resulting in
generation of a sink, transfer failure and the like. Since an O-ring in a
circumferential groove of the nozzle closely comes in contact with a
concave spherical surface while elastically transforming on the entire
circumference, leakage is effectively suppressed even the resin is a
heat-curable resin having a low viscosity.

Claims:

1-4. (canceled)

5. An injection nozzle which is used in a molding apparatus to inject a
resin material by pressing a tip of the injection nozzle against a die,
the injection nozzle comprising:a ring-shaped elastic member provided
around a nozzle hole formed on the tip.

6. The injection nozzle of claim 5,wherein a surface of the tip of the
nozzle to be pressed against the die is flat.

7. The injection nozzle of claim 5,wherein the resin material is an
energy-curable resin.

8. A molding apparatus comprising the injection nozzle of claim 5.

Description:

FIELD OF THE INVENTION

[0001]The present invention relates to a molding technique, particularly
to an injection nozzle used in a molding apparatus suitable for
production of a high-precision product, and a molding apparatus.

BACKGROUND

[0002]A molding apparatus capable of injection molding of high-precision
optical elements using a resin material is known. In the general molding
apparatus, as shown in Patent Literature 1, a movable die is mounted on a
movable side die plate, and pressure is applied to it against the fixed
die mounted on a fixed die plate. Then, an injection nozzle is made
closely come in contact with the outside of the fixed die, and resin is
injected into the cavity of the die through the nozzle hole of the
injection nozzle and the sprue of the fixed die, whereby the resin is
solidified, and a molded product is obtained. [0003]Patent Literature 1:
Japanese Unexamined Patent Application Publication No. 2006-272558

DISCLOSURE OF INVENTION

Problems to be Solved by the Invention

[0004]In the general molding apparatus of the conventional art, as shown
in FIG. 5, the tip of the injection nozzle EN for injecting resin into
the die has a convex spherical surface, and a concave spherical surface
having a radius greater than that of the convex spherical surface is
formed around the open end of the sprue SP of the fixed die DP. When the
injection nozzle EN is pressed against the fixed die DP, both spherical
surfaces fit to each other (referred to as a spherical surface
reception), whereby circular line contact is formed. Thus, the pressure
generated between the injection nozzle EN and fixed die DP can be
concentrated on a narrow contact portion. This allows a high contact
pressure to be generated, and therefore, the nozzle hole AP of the
injection nozzle EN and sprue SP can be communicated with each other to
suppress leakage of resin from therebetween.

[0005]Incidentally, there is an attempt to perform molding operations
using the energy-curable resin as represented by heat-curable resin or
photo-curable resin. The energy-curable resin is cured when energy is
given from the outside. Unlike the regular thermoplastic resin, after
having been once cured, the energy-curable resin is hardly subjected to
transformation when exposed to a high temperature.

[0006]However, one of the problems with the molding operation performed by
using the energy-curable resin as represented by heat-curable resin or
photo-curable resin is that the energy-curable resin is generally a
liquid of low viscosity at the normal temperature, and therefore, there
may be a leakage from between the injection nozzle hole and sprue if a
conventional spherical surface receiver is employed. To put it more
specifically, when the injection nozzle EN having a shape shown in FIG. 5
is employed, the line contact permits the resin material of low viscosity
to easily leak out and the injection pressure cannot be increased. As a
result, the resin material fails to increase the own pressure inside the
molding cavity. This leads to an increased curing shrinkage rate, and a
reduced geometric transferability. Thus, high-precision molding operation
cannot be achieved. Further, resin leakage is characterized by lower
repeatability. This tends to increase variation in the injection
pressure, to reduce the reproducibility of the molded product and to
increase dimensional variations.

[0007]As a test which the present inventors conducted, for example, in the
combination of the injection nozzle and fixed die using the conventional
spherical surface reception, injection operation was performed using the
heat-curable resin having a viscosity of 250 mPas. A resin leakage
occurred at the combination part, and the injection pressure could be
increased only to the level of 5 MPa. This value is much lower than the
injection pressure of about 100 MPa which can be achieved when the
injection molding operation is performed using the regular thermoplastic
resin. Thus, the molding shrinkage increases by this difference, and a
sink occurred. This brought about a considerable deterioration in molding
transferability.

[0008]In view of the problems described above, it is an object of the
present invention to provide an injection nozzle and molding apparatus in
which the resin leakage is suppressed and the injection pressure can be
ensured, even when a resin material of lower viscosity is used.

Means for Solving the Problems

[0009]The injection nozzle of the present invention is used in a molding
apparatus and on the injection nozzle whose tip is pressed against a die
to perform injection molding of the resin material, a ring-shaped elastic
member is provided around the nozzle hole formed on the tip.

[0010]The present inventors have found out that, when a ring-shaped
elastic member is installed on the injection nozzle and this injection
nozzle is pressed against the die, the ring-shaped elastic member is
transformed to produce a sealing effect against the resin leakage,
whereby injection pressure can be increased without the resin being
leaked, even when the resin of lower viscosity is utilized.

[0011]To be more specific, in the present invention, a ring-shaped elastic
member is provided around the nozzle hole formed on the tip. Thus, when
the tip is pressed against the die, the ring-shaped elastic member is
transformed to seal the space between the injection nozzle and die, and
effective suppression of resin leakage is provided. This allows the resin
material of high pressure to be pressure-fed from the hole of the
injection nozzle to the die, whereby the injection pressure is increased,
so that high-precision products can be molded.

[0012]According to the specific embodiment of the present invention, the
tip of the nozzle pressed against the die has a flat surface. This can
make the diameter of the nozzle hole or sprue larger than in the case of
the spherical surface reception, and allows the resin material to be
injected for a shorter period of time, and hence, the molding cycle to be
shorter. The injection nozzle having a flat surface is less affected by
the shift with respect to the fixed die as a counterpart. When the die is
mounted on the molding apparatus, this arrangement eliminates the need of
ensuring a strict positioning with respect to the injection nozzle, and
therefore, reduces man hours for setup procedures of die replacement and
others. Further, this arrangement eliminates the need of providing both
the injection nozzle and fixed die with spherical surface receivers that
require high-precision machining, and therefore, reduces machining costs
of each of these parts.

[0013]According to the specific embodiment of the present invention, the
aforementioned resin material is an energy-curable resin. The
energy-curable resin includes a heat-curable resin and ultraviolet
curable resin for example. The heat-curable resin is cured by heating,
and therefore, the liquid heat-curable resin at the normal temperature is
supplied into the heated die, and thereby the heat-curable resin can be
solidified. In the meantime, the ultraviolet curable resin is solidified
by being exposed to ultraviolet rays. After the liquid ultraviolet
curable resin at the normal temperature is supplied into a transparent
die, the resin is exposed to ultraviolet rays from the outside, whereby
the resin is solidified.

Effects of the Invention

[0014]The present invention provides an injection nozzle and molding
apparatus wherein resin leakage is suppressed and the injection pressure
is ensured even when a resin material of low viscosity is used.

BRIEF DESCRIPTION OF THE DRAWINGS

[0015]FIG. 1 is a side view of a molding apparatus of an embodiment of the
present invention.

[0016]FIG. 2 is a perspective view of a molding apparatus of an embodiment
of the present invention.

[0017]FIG. 3 is an enlarged view of the portion indicated by arrow III in
FIG. 1.

[0018]FIG. 4 is the same cross sectional view as FIG. 3, showing a
variation of the embodiment.

[0019]FIG. 5 is a cross sectional view of an injection nozzle and fixed
die according to the prior art.

DESCRIPTION OF REFERENCE NUMERALS

[0020]1. Base

[0021]2. Cylinder plate

[0022]3. Movable side die plate

[0023]4. Fixed side die plate

[0024]5. Tie-bar

[0025]6. Cylinder

[0026]6a. Piston

[0027]7. Movable die

[0028]8. Fixed die

[0029]8a. Sprue

[0030]8b. Spherical surface

[0031]8b'. Flat surface

[0032]9. Traveling table

[0033]10. Injection section

[0034]11, 11'. Injection nozzle

[0035]11a. Nozzle hole

[0036]11b. Spherical surface

[0037]11b'. Flat surface

[0038]11c. Circumferential groove

[0039]12. O-ring

BEST MODE FOR CARRYING OUT THE INVENTION

[0040]Referring to the drawing, the following describes the embodiments of
the present invention. FIG. 1 is a side view of a molding apparatus of an
embodiment of the present invention. FIG. 2 is a perspective view of a
molding apparatus of an embodiment of the present invention. FIG. 3 is an
enlarged view of the portion indicated by arrow III in FIG. 1, in which
the injection nozzle is placed in close contact, and the illustration of
the fixed side die plate is omitted.

[0041]In FIG. 1, a base 1 is mounted on a surface plate (not illustrated).
The upper side of the base 1 is provided with a comparatively thick and
tabular cylinder plate 2, a movable side die plate 3 and a fixed side die
plate 4 in that order from the left in such an arrangement as to be
opposed to one another. Four tie-bars 5 of round shaft form parallel to
the upper surface side of the base 1 are mounted between the cylinder
plate 2 and fixed side die plate 4. The cylinder plate 2 and fixed side
die plate 4 are fixed on the base 1, while the movable side die plate 3
is movable along the tie-bars 5.

[0042]The cylinder plate 2 is provided with a die clamping cylinder 6. The
die clamping piston 6a is connected with the movable side die plate 3. A
movable die 7 is mounted on the movable side die plate 3 on the side of
the fixed side die plate 4, and a fixed die 8 is arranged on the fixed
side die plate 4 on the side of the movable side die plate 3. Although
not illustrated, a molding cavity is formed inside the die-clamped
movable die 7 and fixed die 8. This molding cavity communicates with the
concave spherical surface 8b formed on the side of the fixed side die
plate 4 through the sprue 8a inside the fixed die 8.

[0043]On the base 1, a traveling table 9 is mounted adjacent to the fixed
side die plate 4. An injection section 10 is mounted on the traveling
table 9. The injection section 10 is provided with an injection nozzle 11
that can be seated on the spherical surface 8b of the fixed die 8 through
the through-hole 4a of the fixed side die plate 4.

[0044]In FIG. 3, a concave spherical surface 8b with the sprue 8a of the
fixed die 8 as a center is formed around the sprue 8a. In the meantime,
the injection nozzle 11 has a nozzle hole 11a opened at the tip, and a
convex spherical surface 11b formed around the nozzle hole 11a. The
convex spherical surface 11b having a radius smaller than that of the
concave spherical surface 8b has a circumferential groove 11c around the
nozzle hole 11a. An O-ring 12 as a ring-shaped elastic member is provided
inside the circumferential groove 11c.

[0045]The ring-shaped elastic member is not restricted to the O-ring. It
can be quadrilateral in sectional configuration, or the outside surface
can be shaped conforming to the spherical surface around the sprue 8a
when inserted into the injection nozzle 11.

[0046]At the time of maintenance or adjustment, the injection section 10
is retracted from the fixed side die plate 4, and is away from the fixed
side die plate 4, as shown in FIG. 1. The injection section 10 travels
forward together with the traveling table 9 for the molding. As shown in
FIG. 3, the convex spherical surface 11b at the tip of the injection
nozzle 11 is pressed against the concave spherical surface 8b, whereby
the nozzle hole 11a and sprue 8a communicate with each other. At the same
time, elastically transforming on the entire circumference, the O-ring 12
inside the circumferential groove 11c closely comes in contact with the
concave spherical surface 8b. This ensures sealing of the space between
the spherical surfaces lib and 8a.

[0047]The following describes the operation of the molding apparatus as an
embodiment of the present invention: In the first place, the hydraulic
pressure is applied inside the die clamping cylinder 6. This procedure
allows the die clamping piston 6a to travel to the right in FIG. 1, and
the movable side die plate 3 to be driven to the right. When the movable
side die plate 3 has moved to the right, the movable die 7 is pushed by
this movement and travels to the right to come in close contact with the
fixed die 8.

[0048]When a molten heat-curable resin is supplied from the injection
section 10 under this condition, the heat-curable resin is injected into
the sprue 8a of the fixed die 8 through the nozzle hole 11a of the
injection nozzle 11, and is filled with pressure into the molding cavity
inside the dies 7 and 8 heated by an unillustrated heater through an
unillustrated runner. The heat-curable resin heated on the surfaces of
the dies 7 and 8 is cured in conformity to the shape of the molding
cavity. After curing, the pressure inside the die clamping cylinder 6 is
reduced, and the piston 6a is moved to the left in FIG. 1, whereby the
die can be opened and the molded product can be taken out.

[0049]In such an injection molding operation, it is particularly important
that the injection nozzle 11 and fixed die 8 are kept in close contact
with each other and the resin does not leak. Resin leakage therefrom will
reduce molding pressure, increase molding shrinkage of the resin, and
directly affect the qualities of a molded product because of occurrence
of a sink or transfer failure. In the present embodiment, elastically
transforming on the entire circumference, the O-ring 12 inside the
circumferential groove 11c of the nozzle 11 closely comes in contact with
the concave spherical surface 8b. This ensures effective prevention of
the leakage, even when a resin material of low viscosity is used.

[0050]FIG. 4 is the same cross sectional view as FIG. 3, showing a
variation of the embodiment. In this example, the tip of the injection
nozzle 11' constitutes a flat surface 11b', and the opposed surface on
the fixed die 8' also forms a flat surface 8b'. When the injection nozzle
11' is brought in contact with the fixed die 8', the flat surfaces 11b'
and 8b' are pressed against each other, whereby the nozzle hole 11a
communicates with the sprue 8a. Further, elastically transforming on the
entire circumference, the O-ring 12 inside the circumferential groove 11c
closely comes in contact with the flat surface 8b'. This ensures sealing
of the space between the flat surfaces 11b' and 8b'.

[0051]As described above, when the O-ring 12 is brought in surface contact
with the fixed die 8' by the injection nozzle 11' having a flat surface,
the sealing effect can be drastically improved. Further, when the tip of
the injection nozzle 11' has a flat surface 11b', the diameters of the
nozzle hole 11a and sprue 8a can be made greater than that in the case of
the spherical surface reception. This allows the resin material to be
injected in a shorter period of time, hence, the molding cycle to be
reduced. The injection nozzle 11' having a flat surface is less affected
by the shift with respect to the fixed die 8' as a counterpart. When the
dies 7 and 8 are mounted on the molding apparatus, this arrangement
eliminates the need of ensuring a strict positioning with respect to the
injection nozzle 11', and therefore, reduces the number of man hours for
setup procedures as in die replacement. Further, this arrangement
eliminates the need of providing both the injection nozzle 11' and fixed
die 8' with spherical surface receivers that require high-precision
machining, and therefore, reduces machining costs of each of these parts.

[0052]If the ring-shaped elastic member is made of a resin such as
66-nylon, polyimide resin or polyamide resin characterized by a high
degree of heat resistance and compression strength, the sealing effect
can be effectively improved, but there is no restriction to the type of
resin. Further, the same sealing effect can be obtained when the
ring-shaped elastic member is mounted on the fixed die instead of the
injection nozzle. In this case, when the ring-shaped elastic member is
provided with maintenance, the die must be removed from the die plate. By
contrast, as shown in the aforementioned embodiment, when the ring-shaped
elastic member is mounted on the injection nozzle, the injection nozzle
together with the injection section can be retracted on the conventional
molding apparatus shown in FIGS. 1 and 2. This arrangement preferably
ensures easy procurement of a wide space around the ring-shaped elastic
member for maintenance.

[0053]The present invention has been described with reference to
embodiments. It is to be expressly understood, however, that the present
invention is not restricted thereto. The present invention can be
embodied in a number of variations with appropriate modification or
additions.